The present invention relates to a method and apparatus for treating electrically conductive fluid, that is fluid having some electroconductive capability. More particularly, the present invention relates to a method and apparatus which will prevent the precipitation of solids from water which would tend to form a scale on the inner surface of piping through which the water flows, which will aid in the removal of a previously formed scale, and which will inhibit a compound to which the fluid is exposed from being released into the fluid.
In fluid containment systems, the build-up of iron compounds on the inner surface of piping and on other parts of the system results in an increase in the iron content of the fluid flowing through the system because such iron compounds tend to dissolve into the fluid. Such a release of the iron compounds into the fluid results in a discoloration of the fluid, i.e. the fluid takes on the reddish-brown color of the iron oxide. In order to obtain fluid which is free from an excess of concentration of such iron compounds, e.g. iron oxide, the system must be flushed until the fluid having the excessive concentration of iron oxide flows from the system.
This particular problem is most prevalent and apparent after the system has not been used for several hours, such as when the system is initially put into use each morning after it has been shut down overnight.
Several known apparatus and methods are presently being used to prevent the formation of iron oxide and the resultant discoloration of the fluid. Some methods employ chemicals to simply convert the iron oxide into a colorless form of iron compound. Such methods may be considered ineffective in the sense that although the fluid does not become discolored, nonetheless the iron content level of the fluid remains relatively high. Other known methods and apparatus concentrate on preventing the fluid from taking on a high iron content level or on cleaning the deposited iron compound scale from within the fluid system.
The present inventor has researched and developed methods and apparatus using ionized water to remove a scale, mainly consisting of ferric oxide, which has been deposited on the inner surface of fluid piping. It has been recognized that when ionized water flows through piping having an oxide scale deposited on the inner surface thereof, the oxide scale is converted into a soft hydroxide (ferric hydroxide) which can be gradually removed.
According to one such development, U.S. Pat. No. 4,902,391 discloses a "self-generating" system for ionizing fluids with great efficiency to bring about a descaling effect causing the removal of deposited calcium, magnesium and ferric particles.
As disclosed in U.S. Pat. No. 4,902,391, two electrodes of electrically conductive materials having different electrochemical potentials, e.g. aluminum and carbon electrodes, are used to ionize the fluid in contact therewith owing to the potential of the electrodes. The system is "self-generating" in the sense that because the electrodes are electrically isolated from one another, the electroconductive connection between the electrodes is only established by the fluid to be treated which extends therebetween, thereby providing a system in which no external energy source is required and in which minimum current flow and maximum potential difference between the electrodes was expected. In the developmental research related to the method and apparatus disclosed in U.S. Pat. No. 4,902,391, it was found that reducing the electric current flow through the fluid between the electrodes and achieving a voltage only condition, or potential, provided the best performance.
FIG. 1 shows an essential part of the apparatus disclosed in U.S. Pat. No. 4,902,391. Reference numerals 1 and 2 designate positive and negative electrodes, respectively, of electrically conductive materials (e.g. carbon and aluminum) having different electrochemical potentials. The positive carbon electrode 1 and the negative aluminum electrode 2 are electrically isolated from each other so that no physical or electroconductive connection between the electrodes is established except through the fluid which flows between the electrodes in the direction shown by the arrows. As discussed above, it was found that by providing a condition of maximum voltage potential and minimum current flow, the system was effective in the removal of a scale, particularly the removal of a calcium or magnesium scale.
Such an apparatus is also effective for removing an iron compound scale; however, the action of removing such a scale is relatively slow. Using such an apparatus a period of one month to several months may be required to clean an iron compound scale out of a fluid containment system depending on the thickness of the scale. Apart from the extended period of time required to remove the scale, there is another disadvantage in that a considerable increase remains in the iron oxide particles released into the fluid as the fluid is flushed from the system. Therefore, a relatively long time is required to flush out the system each morning before a clear fluid can be obtained.